This invention relates, in general, to semiconductor devices, and more particularly, to the etching and patterning of substrates or lithographic masks.
X-ray lithographic masks typically comprise a thin membrane that is less than 10 microns thick. An X-ray lithographic mask is conventionally formed by depositing a membrane film such as silicon carbide over all surfaces of a silicon substrate. The silicon carbide film on the bottom side of the silicon substrate is lithographically defined to create a window or to create a plurality of windows, and the silicon carbide film is removed from the window or the plurality of windows to expose the underlying silicon substrate. The exposed portion of the silicon substrate may be etched via simple immersion or by immersion in concert with an immersion fixture. The substrate is immersed in an etchant to remove the exposed portion of the silicon substrate, thereby creating a freestanding membrane film of silicon carbide. This immersion technique, however, is not practical for high volume manufacturing operations because the thin membrane film is easily damaged when the X-ray lithographic mask is placed in or removed from the immersion holders. If immersion fixtures are not used, sacrificial protective layers typically are necessary to protect the front side of the substrate. However, formation and removal of the sacrificial protective layer requires additional processing steps, which decreases throughput. The formation and removal of the sacrificial protective layer additionally results in a large number of defects. If immersion fixtures are used, extra manual handling is essential, but the manual handling compromises operator safety and increases defects. Another drawback of the immersion technique is that the etch bath containing the etchant solution can become contaminated with particles that result from the etching of the silicon substrate. Furthermore, the prior art immersion techniques are not suitable for the manufacturing of very thin membrane structures, such as projection electron beam lithography masks which are fragile in nature.
Accordingly, it would be advantageous to provide an apparatus that can be used to form a lithographic mask that is less likely to damage the thin membrane of the mask. It would also be advantageous if the apparatus reduced the number of particulates in the etch solution, and thus, was more suitable for high volume semiconductor device manufacturing. It would also be advantageous to provide higher throughput and to increase operator safety. An additional advantage would be to provide a manufacturing process suitable for extremely thin and fragile membrane structures.